TM 9-2320-363-20-1CENTRAL TIRE INFLATION SYSTEM (CTIS) (M917A1 AND M917A1 W/MCS)CTIS is used to regulate tire pressure at all wheels. This allows operation of the dump truck on all road surfacesacross a wide variety of terrain, including off road, and when vehicle is stuck due to extreme conditions.CTIS uses air from the dump truck's air system. Air is routed to the wheels via a dedicated pneumatic systemplumbed from the vehicle's wet tank. An Operator Control Panel (OCP) and Electronic Control Unit module is mounted tothe shift tower inside the cab.Four air pressures have been programmed into CTIS:Highway90 psi (at 60 mph overspeed takes effect)Cross-country55 psi (at 40 mph overspeed takes effect)Sand40 psi (at 25 mph overspeed takes effect)Emergency30 psi (at 10 mph overspeed takes effect)When the engine is started, tire pressures will be pressures LAST ACHIEVED when vehicle was operated.Major components of the system are:OCP/Electronic Control UnitThe OCP allows for operator selection of tire pressures based on roadModular unit mounted on theconditions and displays service codes and system status. The ECU isShift TowerThe ECU is the control center for the entire CTIS.Wheel ValvesLocated at each wheel end (at outer wheel of dual wheels). Provides forinflation of tires from the vehicle's air supply via the Pneumatic ControlUnit, and deflation of tires upon system demand.Pneumatic Control UnitA solenoid controlled manifold that receives commands from the ECUand controls the air system. Also contains the pressure transducerwhich transmits pressure readings to the ECU. The unit delivers theproper control signal to theappropriate channel.Pressure SwitchActs as an electronic brake priority switch. It prevents CTIS fromconsuming air from the wet tank until the air brake system is fullycharged. Therefore, CTIS safeguards safe operating pressures in theprimary and secondary tanks.Speed SensorProvides the ECU with vehicle speed information.1-20 Change 3